import React, { Component } from "react";

export default class Count extends Component {
  state = { count: 0 };
  //加
  increment = () => {
    const { value } = this.selectNumber;
    const { count } = this.state;
    this.setState({ count: count + value * 1 });
  };
  //减
  decrament = () => {
    const { value } = this.selectNumber;
    const { count } = this.state;
    this.setState({ count: count - value * 1 });
  };
  //奇数加
  incrementIfOdd = () => {
    const { value } = this.selectNumber;
    const { count } = this.state;
    if (count % 2 !== 0) {
      this.setState({ count: count + value * 1 });
    }
  };
  //异步加
  incrementAsync = () => {
    const { value } = this.selectNumber;
    const { count } = this.state;
    setTimeout(() => {
      this.setState({ count: count + value * 1 });
    }, 500);
  };

  render() {
    return (
      <div>
        <h1>当前求和为：{this.state.count}</h1>
        <select ref={(c) => (this.selectNumber = c)}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>
        &nbsp;
        <button onClick={this.increment}>+</button>&nbsp;
        <button onClick={this.decrament}>-</button>&nbsp;
        <button onClick={this.incrementIfOdd}>当前求和为奇数加</button>&nbsp;
        <button onClick={this.incrementAsync}>异步加</button>&nbsp;
      </div>
    );
  }
}
